Sorry about the empty post above. I clicked on "Submit Message" instead of "Forum Home"

There seems to be a little confusion about the causes of the moisture in the windway of a tin whistle. It is quite simple, you are blowing warm, moist air into the instrument. When the warm air of your breath contacts the cold surface of the instrument, moisture condenses out of the air and forms droplets in the windway. These moisture droplets will partially block the windway causing the problems with the sound described by the OP. As stated in the second post, the droplets are simply water. There are two ways to deal with the problem. The first is to place the soft pad of a finger over the aperture containing the fipple and blow hard to blow the water drops out. The finger over the fipple apperture is to prevent the instrument sounding, but do make sure it is the soft pad of your finger so as to avoid damage to the fipple. With a bigger instrument such as a low whistle or tenor recorder, it might be better to wrap your whole hand round the head of the instrument.

The second method is to suck hard briefly, drawing the water back into your mouth. Some people find this latter a bit repulsive, but it is only water and you produced it in the first place so it won't do you any harm.

All duct flutes (whistles, recorders etc.) are prone to this problem because the narrowness of the windway means that the droplets will bridge the top and bottom of the windway blocking it.

As the instrument is played, the interior of the windway warms up until it approaches the temperature of your breath and the condensation will occur further down the tube beyond the fipple as that section will take longer to warm up so the problem will not occur with a warm instrument. Similarly, warming the head of the instrument up before playing should also reduce problems of condensation in the windway.

The dilute detergent down the windway is a useful dodge (but make sure it is really dilute - 20:1 is suggested as a minimum). The detergent being a surfactant will coat the windway and as the water evaporates a thin film of detergent is left on the windway passage. This will lower the surface tension of the condensing moisture so it in turn forms a film on the windway rather than droplets. Recorder makers Moeck sell little bottles of "Antikondens" detergent ready diluted which works well and is non-toxic and perfume free (the latter a problem with domestic detergents).